A molar mass calculator

You will write a small calculator for the compounds of this lesson. It reads a formula such as Na2B4O7, finds its molar mass and the percentage of one element, and then adds the water of a hydrate.

The idea. The formula tells how many atoms of each element are in a unit. The molar mass is the sum of mass times count. A hydrate such as borax has its water added: $\text{Na}_2\text{B}_4\text{O}_7\cdot 10\text{H}_2\text{O}$.

Your tasks.

1. Complete counts(formula) so that it returns a dictionary of the atoms in a simple formula such as Na2B4O7.
2. Complete molar_mass(formula) so that it uses counts and the table MASS.
3. Complete percent(element, formula) so that it returns the mass percentage of one element.
4. Complete hydrate_mass(formula, water) so that it returns the molar mass of the formula plus that number of water molecules.